Voigtlander vito c shutter repair

Not enough details in your description to answer.
I do suggest that if you want knowledge about leaf shutters, you should take the Nat Cam course on the Learn Camera Repair site.

I guess we're talking about a Compur shutter, yes? The learn Camera Repair site also has a 'how-it-works' brochure and service manuals for Compur shutters.

And then there is this video on YT.

I took apart a Vito b with Compur SVS shutter recently. Luckily all went well for me.

If the Vito b is similar to the Vito c , it needs a dummy film in so the film sprockets can revolve the toothed sprocket wheel just above the negative frame.
The camera can be fooled if you do not have a dummy film.
Open the back, wind the film advance lever a couple of turns, then use your thumb to revolve the sprocket wheel towards the take up spool. It does take a bit of force to move the wheel. The wheel needs turning continuously until a good click is heard.
A push with one thumb, then holding the wheel so it does not turn back give it some more continuous pushing until the click sounds.
Then the shutter is cocked and fired as per normal.

Try the dummy film, that may be the answer.